Technical Field
The invention relates to a wire electric discharge machining device and method that machine a workpiece by generating an electric discharge in a machining gap formed between a wire electrode and the workpiece. Particularly, the invention relates to a wire electric discharge machining device and method that terminate an unintentional short circuit when the unintentional short circuit is detected between a wire electrode and a workpiece.
Description of Related Art
Generally, in a wire electric discharge machining device, a wire electrode is moved relative to a workpiece within a horizontal plane (“xy plane”). Before machining, the wire electrode has to be supported vertically to the xy plane between a pair of wire guides. If necessary, a start hole for passing the wire electrode therethrough is formed in the workpiece. The start hole may be limited to a small size, and a gap (hereinafter referred to as clearance) between the wire electrode and the start hole may be small.
The wire electrode has to be delivered from an upper wire guide to a lower wire guide through the start hole. After the wire electrode is extended between the upper and lower wire guides while the wire electrode has been given a predetermined tension, an unintentional contact between the wire electrode in the start hole and the workpiece may be electrically detected. FIG. 8(a) shows a state where due to such unintentional contact, a machining gap cannot be formed and electric discharge machining cannot be performed. Patent Literature 1 discloses a method of terminating a short circuit by moving a wire electrode 2 within the xy plane relatively to a workpiece 3, as shown in FIG. 8(b).